CVE-2018-8877 in Asuswrt-Merlin
Summary
by MITRE
Information disclosure in Asuswrt-Merlin firmware for ASUS devices older than 384.4 and ASUS firmware before 3.0.0.4.382.50470 for devices allows remote attackers to acquire information on internal network IP address ranges by reading the new_lan_ip variable on the error_page.htm page.
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Analysis
by VulDB Data Team • 04/07/2024
The vulnerability described in CVE-2018-8877 represents a critical information disclosure flaw affecting ASUS router firmware versions prior to specific security patches. This vulnerability resides within the Asuswrt-Merlin firmware ecosystem and impacts ASUS devices running firmware versions older than 384.4, as well as devices with ASUS firmware versions before 3.0.0.4.382.50470. The flaw stems from improper handling of internal network information within the web interface error handling mechanism, specifically exposing internal IP address ranges through the new_lan_ip variable in the error_page.htm page. This issue falls under the CWE-200 category of "Information Exposure" and represents a classic case of sensitive data leakage through web application error pages.
The technical exploitation of this vulnerability occurs when remote attackers can access the error_page.htm page and extract the new_lan_ip variable which contains internal network IP address ranges. This exposure happens because the firmware fails to properly sanitize or validate the information displayed in error pages, allowing attackers to gather network topology information that would normally be restricted to internal system processes. The vulnerability demonstrates poor input validation and output sanitization practices within the web server component of the router firmware, creating an attack surface where internal network information can be accessed without authentication. The flaw specifically targets the web interface error handling mechanism, which typically should not reveal internal system parameters to external users.
The operational impact of this vulnerability is significant as it provides attackers with crucial network topology information that can be used for further reconnaissance and attack planning. By obtaining internal IP address ranges, attackers can map out the internal network structure and potentially identify other network devices, services, or vulnerabilities that exist within the local network. This information disclosure creates a foundation for more sophisticated attacks such as internal network scanning, service enumeration, or targeted attacks against specific internal systems. The vulnerability essentially provides an attacker with a roadmap of the internal network, making subsequent attacks much more effective and potentially leading to complete network compromise. This aligns with ATT&CK technique T1018 for "Remote System Discovery" and T1082 for "Software Discovery" in the context of network reconnaissance.
Mitigation strategies for CVE-2018-8877 require immediate firmware updates to the patched versions mentioned in the vulnerability description. Network administrators should prioritize updating all affected ASUS devices to firmware versions 384.4 or later for Asuswrt-Merlin and 3.0.0.4.382.50470 or later for ASUS firmware. Additionally, implementing network segmentation and access controls can help limit the impact of information disclosure by restricting access to internal network information. The vulnerability highlights the importance of proper error handling in network device web interfaces, emphasizing the need for security-by-design principles where sensitive information is never exposed through error pages or public interfaces. Network monitoring should also be enhanced to detect unusual access patterns to web interface error pages that might indicate exploitation attempts. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for potential exploitation of this and similar information disclosure vulnerabilities.